This disclosure relates to a method for controlling fuel injection of a combustion engine. The method comprises the step of providing at least a first predetermined air-fuel mixture map and determining a first air-fuel ratio based on at least one engine operating parameter and said at least first predetermined air-fuel mixture map. The disclosure also relates to a fuel injection system for a combustion engine, wherein said fuel injection system comprising a control unit and at least a first predetermined air-fuel mixture map. The disclosure is particularly advantageous in the field of diesel engines provided with a smoke limiting control arrangement formed by at least one minimum AFR lock-up map. The method and system can for example be used on diesel engines for trucks, busses, construction vehicles, marine engines, automobiles, or the like.
Vehicle fuel economy may be improved by providing the driver with an economy mode selector. When an economy mode is selected by the driver, the engine is controlled to be less responsive, such that an improved fuel economy can be attained. However, the specific engine control settings that give raise to the less responsive engine in the economy mode generally requires extensive, time consuming and costly additional development of the engine control software. There is thus a need for an improved engine control that removes the above mentioned disadvantages.
The disclosure concerns, according to an aspect thereof, a method for controlling fuel injection of a combustion engine, which method comprises the steps of:
providing at least a first predetermined air-fuel mixture map and determining a first air-fuel ratio based on at least one engine operating parameter and said at least first predetermined air-fuel mixture map,
determining a second air-fuel ratio that is offset with a first constant value from said first air-fuel ratio
determining, if a first operating mode or a second operating mode is selected;
controlling engine fuel injection according to said first air-fuel ratio when a currently requested fueling rate results in a smaller air-fuel ratio than said first air-fuel ratio and said first operating mode is selected; or alternatively
controlling engine fuel injection according to said second air-fuel ratio when a currently requested fueling, rate results in a smaller air-fuel ratio than said second air-fuel ratio and said second operating mode is selected.
The first operating mode may represent a standard default operating mode, whereas the second operating may typically represent a first economy mode.
The method and system is closely associated and partly integrated with an engine smoke limiting control arrangement, and in particular the predetermined minimum allowed air-fuel mixture map, hereinafter referred to as air-fuel ratio (AFR) map, of the smoke limiting control arrangement. This AFR map has been developed for minimizing transient visible smoke out of the engine. Transient visible smoke is a direct result of operating the engine on a low AFR. By defining a minimum allowed AFR level, which consequently corresponds to a maximal allowed fueling, rate, the minimum allowed AFR level may be set large enough to avoid or at least reduce the level of transient visible smoke. The idea is to add a constant offset value to the looked-up AFR value and use this offset AFR value as the minimum allowed AFR level when an engine economy operating mode is selected by the driver.
This solution represents a very cost-effective, straight-forward, and simple solution for creating a complete economy operating mode engine setting. The major part of the engine control system that relates the AFR value and the engine control logic that use this AFR value is already existing, and the only additional software modification is the addition of the constant offset value to the AFR value that is identified using the existing AFR map, as well as a economy operating mode selector and associated output signal processing. Compared with the previously known solution, where possibly an entire new expensive and time-consuming fuel injection map was developed purely for the economy operating mode, or where possibly the vehicle acceleration is limited for all vehicle operating conditions, the new solution according to the present disclosure represents a significant improvement.
This solution is highly flexible. Since the only modification relates to introducing at least one AFR offset value, the offset value itself can be easily changed to fit different vehicles, different operators, different customers, or the like. Two, three or more economy operating modes may also be implemented without almost any further development and testing.
This solution further represents an efficient fuel economy engine setting, that reduces fuel consumption without necessarily evoking the often associated impression of a power less engine. Low AFR values are normally only occurring when the driver desires high engine output (high fueling rate) at times of low air mass flow rate (small amount of available fresh air due to turbo lag, high EGR flow, etc.) into the engine. This situation occurs typically during engine transient condition, i.e. during situations where a large and sudden change in engine output is requested. The engine will in the economy operating mode consequently behave as a conventional strong engine during most of the time, and only reduce engine output during certain engine transient conditions.
The disclosure further relates to a corresponding fuel injection system for a combustion engine, which system exhibits the same advantages as described above.
The method may comprise the steps of determining if a first operating mode, a second operating mode or a third operating mode is selected; determining a third air-fuel ratio that is offset with a second constant value from said first air-fuel ratio, wherein said second constant value is larger than said first constant value; and controlling engine fuel injection according to said third air-fuel ratio when said currently requested fueling rate results in a smaller air-fuel ratio than said third air-fuel ratio and said third operating mode is selected. The first operating mode may represent a standard default operating mode, whereas the second operating may represent a first economy operating mode, and the third operating may represent a second economy operating, mode that is more stringent designed than the basic economy operating mode, i.e. an operating mode that results in a further improved fuel economy.
The method may comprise the step of additionally providing at least a second predetermined air-fuel mixture map, wherein each of said at least first and second air-fuel mixture map corresponds to different predetermined engine operating states, and determining, said first air-fuel ratio based on at least one engine operating parameter and the currently selected air-fuel mixture map. The engine control system may be supplied with several different engine operating, states, such as an increased heat operating state for improved exhaust aftertreatment system regeneration, or a low emission operating state for avoiding that any regulatory torque reduction inducement system will lead to a reduction in maximum available engine torque.
The method may comprise the step of controlling at least an EGR valve for temporarily enabling increased air mass flow rate into the engine when a current air-fuel ratio is within a first constant range of said first air-fuel ratio and said first operating mode is selected, and controlling at least said EGR valve for temporarily enabling increased air mass flow rate into the engine when said current air-fuel ratio is within said first constant range of said second air-fuel ratio and said second operating mode is selected. This arrangement serves to reduce the need for limiting the fueling rate, and is therefore not really a fuel economy improvement feature, but more a measure for maintaining engine output power. Hence, instead of hitting the fueling rate limiter the system strives to initially solve the momentarily high torque request by stopping the EGR flow, and consequently increasing the air mass rate of fresh air.
The term “air-fuel mixture” used herein is considered to encompass all types of definitions relating to air-fuel mixtures at any given moment. It is commonly defined in terms of “air-fuel ratio (AFR)”, i.e. the ratio of air to fuel. A low AFR thus indicates a more rich mixture, and high AFR indicates a more lean mixture. However, many other terms are used for the air-fuel mixture, such as “mixture” alone, “fuel-air ratio (FAR) or lambda. Lambda (λ) is the ratio of actual AFR to stoichiometry for a given mixture.